[PATCH net-next v2 3/6] eth: fbnic: Reset MAC stats

[Jakub Kicinski <kuba@kernel.org>]

From: Mohsin Bashir <mohsin.bashr@gmail.com>

Reset the MAC stats as part of the hardware stats reset to ensure
consistency. Currently, hardware stats are reset during device bring-up
and upon experiencing PCI errors; however, MAC stats are being skipped
during these resets.

When fbnic_reset_hw_stats() is called upon recovering from PCI error,
MAC stats are accessed outside the rtnl_lock. The only other access to
MAC stats is via the ethtool API, which is protected by rtnl_lock. This
can result in concurrent access to MAC stats and a potential race. Protect
the fbnic_reset_hw_stats() call in __fbnic_pm_attach() with rtnl_lock to
avoid this.

Note that fbnic_reset_hw_mac_stats() is called outside the hardware
stats lock which protects access to the fbnic_hw_stats. This is intentional
because MAC stats are fetched from the device outside this lock and are
exclusively read via the ethtool API.

Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 .../net/ethernet/meta/fbnic/fbnic_hw_stats.c  | 22 +++++++++++++++++++
 drivers/net/ethernet/meta/fbnic/fbnic_pci.c   |  2 ++
 2 files changed, 24 insertions(+)

diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_hw_stats.c b/drivers/net/ethernet/meta/fbnic/fbnic_hw_stats.c
index 77182922f018..8aa9a0e286bb 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_hw_stats.c
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_hw_stats.c
@@ -1,6 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) Meta Platforms, Inc. and affiliates. */
 
+#include <linux/rtnetlink.h>
+
 #include "fbnic.h"
 
 static void fbnic_hw_stat_rst32(struct fbnic_dev *fbd, u32 reg,
@@ -510,6 +512,16 @@ static void fbnic_get_pcie_stats_asic64(struct fbnic_dev *fbd,
 			   &pcie->ob_rd_no_np_cred);
 }
 
+static void fbnic_reset_hw_mac_stats(struct fbnic_dev *fbd,
+				     struct fbnic_mac_stats *mac_stats)
+{
+	const struct fbnic_mac *mac = fbd->mac;
+
+	mac->get_eth_mac_stats(fbd, true, &mac_stats->eth_mac);
+	mac->get_eth_ctrl_stats(fbd, true, &mac_stats->eth_ctrl);
+	mac->get_rmon_stats(fbd, true, &mac_stats->rmon);
+}
+
 void fbnic_reset_hw_stats(struct fbnic_dev *fbd)
 {
 	spin_lock(&fbd->hw_stats.lock);
@@ -520,6 +532,16 @@ void fbnic_reset_hw_stats(struct fbnic_dev *fbd)
 	fbnic_reset_hw_rxq_stats(fbd, fbd->hw_stats.hw_q);
 	fbnic_reset_pcie_stats_asic(fbd, &fbd->hw_stats.pcie);
 	spin_unlock(&fbd->hw_stats.lock);
+
+	/* Once registered, the only other access to MAC stats is via the
+	 * ethtool API which is protected by the rtnl_lock. The call to
+	 * fbnic_reset_hw_stats() during PCI recovery is also protected
+	 * by the rtnl_lock hence, we don't need the spinlock to access
+	 * the MAC stats.
+	 */
+	if (fbd->netdev)
+		ASSERT_RTNL();
+	fbnic_reset_hw_mac_stats(fbd, &fbd->hw_stats.mac);
 }
 
 void fbnic_init_hw_stats(struct fbnic_dev *fbd)
diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_pci.c b/drivers/net/ethernet/meta/fbnic/fbnic_pci.c
index 953297f667a2..ef7928b18ac0 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_pci.c
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_pci.c
@@ -491,7 +491,9 @@ static void __fbnic_pm_attach(struct device *dev)
 	struct net_device *netdev = fbd->netdev;
 	struct fbnic_net *fbn;
 
+	rtnl_lock();
 	fbnic_reset_hw_stats(fbd);
+	rtnl_unlock();
 
 	if (fbnic_init_failure(fbd))
 		return;
-- 
2.51.0